The present invention relates to a method of programming nonvolatile memory devices.
In recent years, there has been an increasing demand for nonvolatile memory devices that can be electrically programmed and erased and do not need the refresh function of rewriting data at specific intervals.
The nonvolatile memory cell is an element enabling electrical program/erase operations and is configured to perform the program and erase operations by changing its threshold voltage as electrons are migrated by a strong electric field applied to a thin oxide layer.
The nonvolatile memory device generally includes a memory cell array in which cells for storing data are arranged in matrix form, and a page buffer for writing memory into specific cells of the memory cell array or reading memory stored in specific cells. The page buffer includes a bit line pair connected to a specific memory cell, a register for temporarily storing data to be written into a memory cell array, or reading data of a specific cell from the memory cell array and temporarily storing the read data therein. The page buffer further includes a sensing node for sensing the voltage level of a specific bit line or a specific register, and a bit line selection unit for controlling whether or not to connect a specific bit line to the sensing node.
In the program and verify operations of this nonvolatile memory device, a problem arises because leakage current is generated by a memory cell block on which the program operation has not been performed. Consequently, an under program phenomenon occurs, in which the level of a verify voltage applied to a memory cell block on which the verify operation has been performed is lowered, and, therefore, the threshold voltage of a target program cell is lowered.